2,3-Butanediol (2,3-BDO) is a chemical which has important present and potential industrial applications, e.g. as antifreeze, as raw material for methyl ethyl ketone and 1,3-butadiene manufacturing by dehydration, and even as liquid fuel due to its heating value of 27198 kJ·kg−1 (Flickinger, M. C., Biotechnol. Bioeng. 1980, 22, 27) which is comparable to those of methanol (22081 kJ·kg−1) and ethanol (29055 kJ·kg−1). Other potential applications include the manufacture of printing inks, perfumes, fumigants, moistening and softening agents, explosives and plasticizers, and as a carrier for pharmaceuticals (Xiu, Z. L., Zeng, A. P., Present state and perspective of downstream processing of biologically produced 1,3-propanediol and 2,3-butanediol. Appl. Microbiol. Biotechnol. 2008, 78, 917-926).
Almost the totality of the 2,3-BDO manufacturing processes described are based on fermentation of carbohydrates using many bacterial species as shown by both academic (Xiao-Jun J., He H., Ping-Kai O., Microbial 2,3-butanediol production: A state-of-the-art review. Biotechnology Advances 2011, 29, 351-364) and patent (e.g., WO 2014013330 A2, WO 2013076144 A2, U.S. Pat. No. 8,455,224 B2, US 20130316418 A1, WO 2009151342 A1, EP 1897955 B1, WO2009151342A1, U.S. Pat. No. 7,968,319 B2, U.S. Pat. No. 2,389,263 A, KR20130091080 (A)) literature. All these methods have in common as main drawbacks a very low 2,3-BDO productivity, usually ranging from 1 to 3 g/L/h, and a low 2,3-BDO titer in the final culture broth, usually below 120 g/L, and much more usually below 100 g/L. The latter fact, together with the highly complex chemical composition of the culture broth, lead to cumbersome methods for isolation and purification of 2,3-BDO with the corresponding economic penalties.
There are also some chemical routes for obtaining 2,3-BDO. Thus, in CN 103193596A 2,3-BDO is synthesized from a mixture of an alcohol (e.g., methanol, ethanol, propanol and butanol) and mixed C4 hydrocarbons by oxidation with hydrogen peroxide in the presence of titanium silicalite modified with aluminum oxide as catalyst. However, this process leads to a low 2,3-BDO selectivity of 41%. In JPH0441447 (A) 2,3-BDO is produced by means of photocatalyst by irradiating ethanol with light resulting from a high-intensity ultraviolet laser in the presence of hydrogen peroxide, process which is not industrially feasible.
The process of the present invention overcomes the above mentioned drawbacks by using as raw material acetoin (3-hydroxybutanone), an α-hydroxy ketone, which is reduced with hydrogen to 2,3-BDO using a heterogeneous hydrogenation catalyst optionally in the presence of a solvent.
In Org. Lett., 2007, 9 (13), 2565-2567, T. Ohkuma et al describe the asymmetric hydrogenation of a series of α-hydroxy aromatic ketones in methanol catalyzed by Cp*Ir(OTf)(MsDPEN) (MsDPEN=N-(methanesulfonyl)-1,2-diphenylenediamine). However, this procedure for α-hydroxy aromatic ketones hydrogenation has some drawbacks like the use of a homogeneous catalyst which makes much more complex the isolation of the product.
In EP 0405956A1 a process for the catalytic hydrogenation of α-hydroxy ketones is described. Dihydroxyacetone and eruthrulose are the only α-hydroxy ketones mentioned, which are reduced to the corresponding alcohols, e.g. glycerol if dihydroxyacetone is the starting α-hydroxy ketone, in a heterogeneous liquid phase reaction medium which contains a carboxylic acid as strong selectivity enhancer to the alcohol. If no carboxylic acid is added selectivity is lower than 75%.
Surprisingly, the present inventors have found that in the process of the present invention a selectivity higher than 90% is achieved with no carboxylic acid added, which is not apparent for a person skilled in the art. This leads to a very important industrial additional advantage because isolation of the target chemical, 2,3-butanediol in the present invention, can be carried out in a much easier and cheap way. On the other hand, the use of carboxylic acids as selectivity enhancers as those used in EP 0405956A1, citric and acetic acids, can affect negatively to the stability of the metal catalyst employed, in particular to catalysts comprising a Group VIII metal as those used in EP 0405956A1. This is because the carboxylic acids, like, e.g., citric acid act as chelating agents and, consequently, losses of metal catalyst from the support by lixiviation can easily occur. This important drawback is also avoided in the process of the present invention as shown in examples 37 and 38 in which a catalyst was repeatedly recycled with no loss in metal content.